Piezoelectric thin-film element, ink-jet head using the same, and method for manufacture thereof

ABSTRACT

A piezoelectric element with stable and excellent piezoelectric properties is made by: a step of forming a diaphragm  30  ( 31, 32 ) on a substrate  20  (S1); a step of forming a bottom electrode  33  on the diaphragm  30  (S2); a step of forming a first piezoelectric layer  43   a  on the bottom electrode  33  (S3); a step of patterning both the piezoelectric layer  43   a  and the bottom electrode  33  (S4); a step of forming a second piezoelectric layer on the piezoelectric layer  43   a  and on the diaphragm  30  to mature a piezoelectric film  43  (S5); and a step of forming a top electrode  44  on the piezoelectric film  43  (S6).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a piezoelectric element havingan electromechanical conversion function. In particular, the presentinvention relates to a piezoelectric element that makes it possible toobtain an excellent piezoelectric characteristic when used in an ink-jetrecording head, a method for the manufacture thereof, and an ink-jetrecording head and a printer using such piezoelectric elements.

[0003] 2. Description of the Related Art

[0004] Ink-jet recording heads use piezoelectric elements as drivingmechanism for ink ejection in printers. The piezoelectric elementsusually comprise a piezoelectric thin film and a top electrode and abottom electrode disposed so as to sandwich the film.

[0005] Piezoelectric elements with improved characteristics have beendeveloped by regulating the crystal structure of a thin film composed oflead zirconium titanate (PZT) or forming Ti nuclei on the bottomelectrode. For example, Japanese Patent Application Laid-open No.H10-81016 disclosed a PZT thin film provided with a rhombohedral crystalstructure and the prescribed orientation degree. Furthermore, JapanesePatent Application Laid-open No. H8-335676 disclosed a piezoelectricelement in which a titanium nucleus was formed on an Ir bottomelectrode.

[0006] However, the problem associated with the conventionalpiezoelectric elements was that piezoelectric films with prescribedorientation degree were difficult to obtain with good stability andreproducibility. Such piezoelectric elements could not provide stableand good piezoelectric characteristics and accounted for insufficientprinting performance of ink-jet recording heads or printers.

[0007] The prescribed orientation degree of piezoelectric film wasespecially difficult to obtain with good stability and reproducibilitywhen a bottom electrode formed on a diaphragm was patterned to theprescribed shape and then a piezoelectric film was formed on the bottomelectrode. Another problem was that the thickness of the bottomelectrode became non-uniform and the crystals of the piezoelectric filmbecame discontinuous in the vicinity of the patterning boundary ofbottom electrode.

SUMMARY OF THE INVENTION

[0008] Accordingly, it is an object of the present invention to providea piezoelectric element with stable and good piezoelectriccharacteristic by obtaining the prescribed orientation degree ofpiezoelectric film with good stability and reproducibility and also amethod for the manufacture of such a piezoelectric element. Anotherobject of the present invention is to provide a piezoelectric elementdemonstrating excellent characteristics by improving the uniformity ofthe bottom electrode thickness and eliminating the discontinuity ofcrystals of the piezoelectric film and also a method for the manufactureof such a piezoelectric element.

[0009] Still another object is to provide an ink-jet recording heademploying the aforesaid piezoelectric elements as ink ejection drivemechanism, a method for the manufacture thereof, and an ink-jet printer.

[0010] A method for the manufacture of a piezoelectric element inaccordance with the present invention comprises a step of forming adiaphragm on a substrate, a step of forming a bottom electrode on thediaphragm, a step of forming a first piezoelectric layer constituting apart of a piezoelectric film on the bottom electrode, a step ofpatterning the first piezoelectric layer and the bottom electrode to theprescribed shape, a step of forming a second piezoelectric layerconstituting another part of the piezoelectric film on the firstpiezoelectric layer that was left by the patterning and the diaphragmfrom which the first piezoelectric layer was removed, and a step offorming a top electrode on the piezoelectric film.

[0011] Forming a piezoelectric film in two stages makes it possible toform PZT having stable 100 plane orientation degree which is notaffected by humidity or the like. Furthermore, the non-uniformity of thebottom electrode thickness and discontinuity of piezoelectric crystalscan be prevented.

[0012] Another method for the manufacture of a piezoelectric element inaccordance with the present invention comprises a step of forming adiaphragm on a substrate, a step of forming a bottom electrode on thediaphragm, a step of forming a first Ti layer on the bottom electrode, astep of patterning the bottom electrode to the prescribed shape, a stepof forming a second Ti layer on the bottom electrode that was left bythe patterning and the diaphragm from which the bottom electrode wasremoved, a step of forming a piezoelectric film on the bottom electrodeon which the second Ti layer was formed, and a step of forming a topelectrode on the piezoelectric film.

[0013] Forming a Ti layer in two stages makes it possible to form apiezoelectric film having a stable 100 plane orientation degree which isnot affected by humidity or the like.

[0014] A method for the manufacture of an ink-jet recording head inaccordance with the present invention comprises a step of etching thesubstrate of the piezoelectric element obtained by the above-describedmethod and forming pressure chambers and a step of forming a nozzleplate covering the pressure chambers.

[0015] In the piezoelectric element in accordance with the presentinvention, a diaphragm, a bottom electrode, a piezoelectric film, and atop electrode are successively stacked on a substrate. The bottomelectrode is patterned to a prescribed shape, and the piezoelectric filmis formed on the bottom electrode that was left by the patterning andthe diaphragm from which the bottom electrode was removed. The number oflayers in the portion of the piezoelectric film, which was formed on thebottom electrode that was left by the patterning, is greater than thatin the portion formed on the diaphragm.

[0016] Furthermore, in another piezoelectric element in accordance withthe present invention, the piezoelectric film is formed on the bottomelectrode left by the patterning and on the diaphragm from which thebottom electrode was removed and the thickness of the bottom electrodeis uniform.

[0017] In still another piezoelectric element in accordance with thepresent invention, the piezoelectric film is formed on the bottomelectrodes left by the patterning and on the diaphragm from which thebottom electrode was removed. The portion of the piezoelectric film thatwas formed on the diaphragm has a prescribed orientation.

[0018] In the above-described piezoelectric element, a portion of thepiezoelectric film, which was formed on the bottom electrode that wasleft by the patterning, preferably has a 100 plane orientation degree ofno less than 70%.

[0019] The ink-jet recording head in accordance with the presentinvention comprises the above-described piezoelectric elements, pressurechambers whose internal volume changes under the effect of mechanicaldisplacement of the piezoelectric elements, and ejection openings linkedto the pressure chambers and ejecting ink droplets.

[0020] The ink-jet printer in accordance with the present inventioncomprises the above-described ink-jet recording head in a printingmechanism.

[0021] The term “100 plane orientation degree” used in the presentspecification means a ratio of I(100) to a sum of I(100), I(110), andI(111), where I(XYZ) stands for a diffraction intensity of a peak (2θ)corresponding to a XYZ plane when a CuKα beam is used in the X raywide-angle diffraction method.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a perspective view illustrating a structure of theprinter using the piezoelectric element of the present invention;

[0023]FIG. 2 illustrates a structure of the ink-jet recording headprovided with the piezoelectric element;

[0024]FIG. 3A is an enlarged plan view of a piezoelectric elementportion of the ink-jet recording head and

[0025]FIG. 3B is a cross-sectional view along the i-i line therein;

[0026]FIG. 4 is a cross-sectional view along the ii-ii line in FIG. 3A;

[0027]FIG. 5 is a cross-sectional schematic view illustrating a methodfor the manufacture of the piezoelectric element and the ink-jetrecording head of the first embodiment;

[0028]FIG. 6 is a cross-sectional schematic view illustrating a methodfor the manufacture of the piezoelectric element and the ink-jetrecording head of the first embodiment;

[0029]FIG. 7 is a cross-sectional SEM microphotograph of thepiezoelectric element obtained by the above-mentioned manufacturingmethod;

[0030]FIG. 8 is a model view of FIG. 7;

[0031]FIG. 9 is a cross-sectional SEM microphotograph of thepiezoelectric element of a comparative example;

[0032]FIG. 10 is a model view of FIG. 9; and

[0033]FIG. 11 is a cross-sectional schematic view illustrating a methodfor the manufacture of the piezoelectric element and the ink-jetrecording head of the second embodiment, this figure showing the part ofthe process corresponding to FIG. 5 of the first embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Preferred embodiments of the present invention will be describedbelow with reference to the appended drawings.

[0035] (Entire Configuration of Ink-Jet Printer)

[0036]FIG. 1 is a perspective view illustrating a structure of theprinter using the piezoelectric element. In this printer, a tray 3, arelease opening 4, and a control button 9 are provided in a body 2.Furthermore, an ink-jet recording head 1, a feeding mechanism 6, and acontrol circuit 8 are provided inside the body 2.

[0037] The ink-jet recording head 1 comprises a plurality ofpiezoelectric elements formed on a substrate and is composed so that itcan eject ink from a nozzle according to an ejection signal suppliedfrom the control circuit 8.

[0038] The body 2 is a case of the printer. The feeding mechanism 6 isdisposed in a position in which paper 5 can be fed from the tray 3, andthe ink-jet recording head 1 is disposed so that printing can beconducted on the paper 5. The configuration of the tray 3 allows forfeeding the paper 5 before the printing to the feeding mechanism 6. Therelease opening 4 is an output opening for releasing the paper 5 uponcompletion of printing.

[0039] The feeding mechanism 6 comprises a motor 600, rollers 601, 602,and another mechanical structure which is not shown in the figures. Themotor 600 can rotate in response to a drive signal supplied from thecontrol circuit 8. The mechanical structure can transmit the rotatingforce of the motor 600 to the rollers 601, 602. The rollers 601, 602rotate when the rotating force of the motor 600 is transmitted. Thisrotation of the rollers pulls in the paper 5 located in the tray 3 andfeeds the paper for printing with the head 1.

[0040] The control circuit 8 comprises CPU, ROM, RAM, and interfacecircuits that are not shown in the figure. The control circuit 8 cansupply the drive signal to the feeding mechanism 6 or the ejectionsignal to the ink-jet recording head 1 according to printing informationsupplied from a computer via a connector (not shown in the figures).Furthermore, the control circuit 8 also sets and resets the operationmode according to operation signals from the control panel 9.

[0041] The printer of the present embodiment is a high-performanceprinter because it comprises the below-described ink-jet recording headhaving stable and high piezoelectric characteristics and demonstratinggood printing performance.

[0042] (Configuration of the Ink-Jet Recording Head)

[0043]FIG. 2 illustrates a structure of the ink-jet recording headcomprising the piezoelectric element. The ink-jet recording head 1, asshown in the figure, comprises a nozzle plate 10, a pressure chambersubstrate 20, and a diaphragm 30.

[0044] The pressure chamber substrate 20 comprises cavities (pressurechambers) 21, side walls (partitions) 22, a reservoir 23, and supplyopenings 24. The cavities 21 are the spaces that are formed by etchingin a substrate such as silicon substrate for storing ink to be ejected.The side walls 22 are formed so as to provide partitions between thecavities 21. The reservoir 23 is a common channel for filling thecavities 21 with the ink. The supply openings 24 are formed so that theink can be introduced from the reservoir 23 to the cavities 21.

[0045] The nozzle plate 10 is attached on one surface of the pressurechamber substrate 20 so that nozzle holes 11 formed therein are disposedin positions corresponding to respective cavities 21 provided in thepressure chamber substrate 20. The pressure chamber substrate 20 havingthe nozzle plate 10 attached thereto is further enclosed in a case 25 toform the ink-jet recording head 1.

[0046] The diaphragm 30 is attached to the other surface of the pressurechamber substrate 20. Piezoelectric elements (not shown in the figure)are provided on the diaphragm 30. An ink tank opening (not shown in thefigure) is provided in the diaphragm 30, and the ink that was stored inthe ink tank (not shown in the figures) can be supplied into thepressure chamber substrate 20.

[0047] (Configuration of Piezoelectric Element)

[0048]FIG. 3A is an expanded plan view of a piezoelectric elementportion of the ink-jet recording head and FIG. 3B is a cross-sectionalview thereof along the i-i line. FIG. 4 is a cross-sectional view alongthe ii-ii line in FIG. 3A.

[0049] As shown in those figures, the piezoelectric element is producedby successively stacking a ZrO₂ film 32, a bottom electrode 33, apiezoelectric film 43, and a top electrode 44 on an insulating film 31.

[0050] The insulating film 31 is formed on the pressure chambersubstrate 20 composed, for example, of single-crystal silicon with athickness of 220 μm. Preferably, a film composed of silicon oxide (SiO₂)is formed to a thickness of 1.0 μm.

[0051] The ZrO₂ film 32 is a layer providing the elasticity; it isintegrated with the insulating film 31, constituting a diaphragm 30. Forthe ZrO₂ film 32 to have a function of providing the elasticity, itpreferably has a thickness of no less than 200 nm and no more than 800nm.

[0052] An adhesive layer (not shown in the figures) consisting of ametal, preferably, titanium or chromium, may be provided for bonding theZrO₂ film 32 and the bottom electrode 33. When the adhesive layer isprovided, the preferred thickness thereof is no less than 10 nm.

[0053] The bottom electrode 33 has a layered structure. In this case thelayers contain Pt and Ir. For example, the electrode has anIr-containing layer/Pt-containing layer/Ir-containing layer structure.The thickness of the entire bottom electrode 33 is, for example, 100 nm.No specific limitation is placed on the layered structure of the bottomelectrode 33. Thus, it may have a two-layer configuration ofIr-containing layer/Pt-containing layer, or a two-layer structure ofPt-containing layer/Ir-containing layer. Furthermore, the bottomelectrode 33 may also be composed only of an Ir-containing layer.

[0054] The piezoelectric film 43 is a piezoelectric polycrystallineceramic. The piezoelectric film 43 is preferably composed of aferroelectric piezoelectric material such as lead zirconium titanate(PZT), or a material obtained by adding a metal oxide such as niobiumoxide, nickel oxide, or magnesium oxide thereto. The composition of thepiezoelectric film 43 is selected appropriately by taking thecharacteristics and application of the piezoelectric element intoaccount. Specific preferred examples include lead titanate, leadzirconium titanate, lead zirconate, lead lanthanum titanate, leadlanthanum zirconate titanate, or lead zirconium titanate magnesiumniobate. Furthermore, a film with excellent piezoelectriccharacteristics can also be obtained by adding an appropriate amount ofniobium to lead titanate or lead zirconate.

[0055] A portion of the piezoelectric film 43 which is formed on thebottom electrode 33 preferably has a 100 plane orientation degree of noless than 70% and no more than 100%, more preferably, no less than 80%in order to obtain good piezoelectric characteristics. It is furtherpreferred that a 110 plane orientation degree is no more than 10%, witha 111 plane orientation degree assuming the balance. The sum of the 100plane orientation degree, the 110 plane orientation degree, and the 111plane orientation degree is 100%. The thickness of the piezoelectricfilm 43 is, for example, no less than 1000 nm and no more than 1500 nm.

[0056] The top electrode 44 is an electrode forming a pair with thebottom electrode 33; preferably, it is composed of Pt or Ir. Thethickness of the top electrode 44 is preferably about 50 nm.

[0057] The bottom electrode 33 is common for all piezoelectric elements.By contrast, a wiring electrode 33 a is positioned in the same height asthe bottom electrode 33, but is separated from the bottom electrode 33and the other wiring electrodes 33 a. The wiring electrode 33 a can beelectrically connected to the top electrode 44 via a strip electrode 45.

[0058] (Operation of Ink-Jet Recording Head)

[0059] Printing operation with the ink-jet recording head 1 of theabove-described configuration will be explained below. If a drive signalis received from the control circuit 8, the feeding mechanism 6 isactivated and paper 5 is transported to the position where printing canbe conducted with the head 1. When no ejection signal is supplied fromthe control circuit 8 and voltage is not applied between the bottomelectrode 33 and the top electrode 44 of a piezoelectric element, thepiezoelectric film 43 is not subjected to deformation. No pressurechanges occur in the cavity 21 provided with the piezoelectric elementthat has not been supplied with the ejection signal, and ink drops arenot ejected from the nozzle hole 11 of this cavity.

[0060] On the other hand, when an ejection signal is supplied from thecontrol circuit 8 and a constant voltage is applied between the bottomelectrode 33 and the top electrode 44 of the piezoelectric element, thepiezoelectric film 43 is subjected to deformation. In the cavity 21provided with the piezoelectric element that was supplied with theejection signal, the diaphragm 30 greatly deflects. As a result, thepressure inside the cavity 21 rises instantaneously and an ink dropletis ejected from the nozzle hole 11. Printing of any symbols or drawingscan be conducted by individually supplying the ejection signals topiezoelectric elements in the head which are located in positions inwhich printing is desired.

[0061] (Manufacturing Method of the First Embodiment)

[0062] A method for the manufacture of the piezoelectric element inaccordance with the present invention will be described below. FIGS. 5and 6 are cross-sectional schematic views illustrating a method for themanufacture of the piezoelectric element and the ink-jet recording headof the first embodiment.

[0063] Step of Forming a Diaphragm (S1)

[0064] An insulating film 31 is formed on a silicon substrate 20. Thethickness of the silicon substrate 20 is, for example, about 200 μm. Inthe manufacture of the insulating film, a high-temperature treatment isconducted in an oxidizing atmosphere composed of oxygen or steam and afilm of silicon dioxide (SiO₂) with a thickness of about 1 μm is formed.Besides the usually used thermal oxidation method, a CVD method can beused in this step.

[0065] Then, a ZrO₂ film 32 with a thickness of about 400 nm is formedon the insulating film 31. The ZrO₂ film 32 is obtained by growing a Zrlayer by sputtering or vacuum deposition and then treating it at a hightemperature in an oxygen atmosphere.

[0066] Step of Forming a Bottom Electrode (S2)

[0067] A bottom electrode 33 is then formed on the ZrO₂ film 32. Thestep of forming the bottom electrode 33, for example, comprises a stepof forming a third layer containing Ir, a step of forming a second layercontaining Pt on the third layer, and a step of forming a first layercontaining Ir on the second layer.

[0068] The first, second, and third layers are formed by depositing Iror Pt on the ZrO₂ film 32 by sputtering or the like. Prior to formingthe bottom electrode 33, an adhesive layer (not shown in the figures)consisting of titanium or chromium may be formed by sputtering or vapordeposition.

[0069] It is preferred that once the bottom electrode 33 has beenformed, a Ti layer (nucleus) be formed in succession on the bottomelectrode 33. The Ti layer is formed to a thickness of no less than 3 nmto no more than 20 nm, for example, by sputtering. The Ti layer isformed as a uniform film on the bottom electrode 33, but it may alsohave an island-like structure.

[0070] Step of Forming a First Piezoelectric Layer (S3)

[0071] A piezoelectric film is then formed on the bottom electrode 33.In the first step, a first piezoelectric layer 43 a is formed to have athickness no more than the desired thickness of piezoelectric film 43,or preferably no more than half of the desired thickness. For example,when the piezoelectric film 43 with a total film thickness of 1.5 μm iscomposed of 7 layers, at least one piezoelectric layer 43 a with athickness of 0.2 μm is formed. A plurality of first layers in which thetotal thickness is less than half of the total thickness of thepiezoelectric film 43 may also be formed.

[0072] More specifically, a piezoelectric precursor film is formed by asol-gel method. Thus, a sol composed of an organic metal alkoxidesolution is coated on the bottom electrode by a coating process such asspin coating. Then, the coating is dried for a prescribed time period ata prescribed temperature to evaporate the solvent. The drying isfollowed by pyrolyzing for a prescribed time period at a prescribedtemperature in air for thermal decomposition of organic ligandscoordinated with the metal and formation of metal oxide. Thepiezoelectric precursor films are stacked by repeating the coating,drying, and pyrolyzing steps several times, for example, two times. As aresult of drying and pyrolyzing, metal alkoxide and acetic acid saltpresent in the solution form a metal/oxygen/metal network via thermaldecomposition of ligands.

[0073] The piezoelectric precursor films are then annealed tocrystallize the piezoelectric layer. Due to annealing, the piezoelectricprecursor film changes its structure from amorphous to a rhombohedralcrystal structure and changes to a layer demonstrating anelectromechanical conversion effect. Conducting the above-describedsteps of forming and annealing the piezoelectric precursor film in onecycle produces a first piezoelectric layer 43 a consisting of one layer.

[0074] The piezoelectric layer 43 a thus formed is affected by thecomposition of the bottom electrode 33 and the aforesaid Ti layer, andits 100 plane orientation degree measured by X ray diffractionwide-angle method will be about 80%.

[0075] By the above-described annealing, the bottom electrode 33 is alsopartially oxidized and PZT components partially diffuse and then thethickness of the bottom electrode increases. With a method for forming apiezoelectric film after patterning of the bottom electrode, theincrease in thickness in the vicinity of patterning boundary of thebottom electrode is typically smaller than the other portion of thebottom electrode, which results in a non-uniform thickness of the bottomelectrode. However, with the method of the present embodiment, thepiezoelectric layer 43 a is formed prior to patterning of the bottomelectrode 33. Therefore, the thickness of the bottom electrode overallincreases and does not become non-uniform.

[0076] Patterning of the bottom electrode and the piezoelectric layer(S4)

[0077] The piezoelectric layer 43 a is then masked according to adesired shape, and patterning of the piezoelectric layer 43 a and thebottom electrode 33 is conducted by etching on the outside thereof. As aresult, the wiring electrode 33 a is separated from the bottom electrode33. More specifically, a resist material of uniform thickness is coatedon the piezoelectric layer 43 a by a spinner method, spray method, orthe like (not shown in the figure). Then a mask is formed to aprescribed shape, followed by the formation of a resist pattern on thepiezoelectric layer by exposure and development (not shown in thefigure). The piezoelectric layer 43 a and the bottom electrode 33 areetched out by ion milling or dry etching method usually used thereforand the ZrO₂ film 32 is exposed.

[0078] Then, a Ti layer (nucleus) is further formed on the piezoelectriclayer 43 a and the ZrO₂ film 32 by a sputtering method or the like. TheTi layer formed at this stage preferably has a thickness of no less than1 nm and no more than 4 nm. If the thickness of the Ti layer is lessthan 1 nm, the effect of the seed layer is small. If the thickness isabove 4 nm, the formation of PZT crystals is broken on the Ti layer as aboundary and there is a possibility of crystals being discontinuous orof interlayer peeling. It is even more preferred that the Ti layer havea thickness of about 2 nm.

[0079] Step of forming a second piezoelectric layer (S5)

[0080] A step of forming second piezoelectric layers on the firstpiezoelectric layer 43 a is then implemented. In this step, theoperations of coating a piezoelectric precursor and annealing areimplemented by the same method as in the step of forming the first layer43 a and it is repeated, for example, six times till the desiredthickness of piezoelectric film is obtained. As a result, apiezoelectric film 43 with a total thickness of 1.5 μm is formed.

[0081] In the piezoelectric film 43 thus formed, a portion above thebottom electrode 33 consists of a total of seven layers because thesecond piezoelectric layers obtained after the patterning step is formedon the first piezoelectric layer 43 a. A portion formed in the zone inwhich the first piezoelectric layer 43 a and the bottom electrode 33were removed by patterning and where the ZrO₂ film 32 was exposedconsists of a total of six layers. Thus, in the piezoelectric film 43formed by the method of the present embodiment, the portion formed onthe bottom electrode 33 that was left by patterning has a larger numberof layers than the portion formed on the diaphragm 30. Furthermore, inthe present embodiment, the total thickness of the second piezoelectriclayers is greater than the thickness of first piezoelectric layer.Therefore, the portion of the piezoelectric film on the diaphragm 30from which the bottom electrode was removed can be formed to have asufficient thickness.

[0082] By annealing in the step of forming the first piezoelectriclayer, the bottom electrode 33 is partially oxidized and the diffusionof PZT components occurs which results in an overall increase in filmthickness. For this reason, the thickness of the bottom electrode doesnot further increase in the step of forming the second piezoelectriclayers. Therefore, the thickness of the bottom electrode 33 does notbecome non-uniform. Moreover, in the piezoelectric film 43 in thevicinity of patterning boundary of the bottom electrode 33, no cracksare introduced by changes in the thickness of the bottom electrode 33and the crystals do not become discontinuous in the film surfacedirection.

[0083] As for the piezoelectric film 43, a portion above the bottomelectrode 33 is affected by the first piezoelectric layer 43 a andbecomes a piezoelectric film with a 100 plane orientation degreemeasured by an X ray diffraction wide-angle method of about 80%.Furthermore, a portion formed in the zone from which the bottomelectrode 33 was removed by patterning and where the ZrO₂ film 32 wasexposed is affected by the Ti layer and has a large orientation in 111plane.

[0084] Furthermore, the thickness of the Ti layer formed after thepatterning step (S4) was no more than 4 nm. As a result, the crystalstructure is continuous in the film thickness direction between thefirst piezoelectric layer 43 a and the second piezoelectric layer andpeeling between the first and second layers is inhibited. For thisreason, a highly reliable piezoelectric film 43 can be obtained.

[0085]FIG. 7 is a cross-sectional SEM microphotograph of thepiezoelectric element in which the thickness of the Ti layer formedafter the patterning step (S4) in the present embodiment was 2 nm, FIG.8 is the model thereof. FIG. 9 is a cross-sectional SEM microphotographof the piezoelectric element in which the thickness of the Ti layerformed after the patterning step was 5 nm, this element representing acomparative example, FIG. 10 is the model thereof. Thesemicrophotographs demonstrate that the PZT crystal structure wascontinuous when the thickness of the Ti layer was 2 nm. By contrast,when the thickness of the Ti layer was 5 nm, a discontinuous portionappeared between the PZT layers formed before and after the patterningstep. The discontinuous portion has a less continuity of crystals thanthe continuities between the other PZT layers.

[0086] Step of Forming a Top Electrode (S6)

[0087] A top electrode 44 is formed by an electron beam depositionmethod or a sputtering method on the piezoelectric film 43. Platinum(Pt), iridium (Ir), or other metal is used as the top electrode 44 andthe film is formed to a thickness of 50 nm.

[0088] Step of Patterning the Piezoelectric Film and the Top Electrode(S7)

[0089] The piezoelectric film 43 and the top electrode 44 are patternedto a prescribed shape of the piezoelectric element. More specifically, aresist is spin-coated on the top electrode 44 and patterned by exposureand development according to positions in which the pressure chambershave to be made. The remaining resist is used as a mask and the topelectrode 44 and the piezoelectric film 43 are etched by ion milling orthe like. The piezoelectric element 40 is formed by the above-describedsteps.

[0090] Step of Forming a Strip Electrode (S8)

[0091] Then, a strip electrode 45 electrically connecting the topelectrode 44 and the wiring electrode 33 a is formed. Gold, which has alow electric resistance and a low rigidity, is preferred as a materialfor the strip electrode 45. Examples of other preferred metals includealuminum and copper. The strip electrode 45 is formed to a thickness ofabout 0.2 μm and pattering is conducted so as to leave a conductiveportion between the top electrode 44 and the wiring electrode 33 a.

[0092] Step of Forming Pressure Chambers (S9)

[0093] Then, pressure chambers 21 are formed by anisotropic etchingusing an active gas, such as anisotropic etching or a parallel platereactive ion etching, on the other surface of the pressure chambersubstrate 20 where the piezoelectric elements 40 were formed. Portionsthat were not etched out serve as side walls 22.

[0094] Step of bonding a nozzle plate (S10)

[0095] Finally, a nozzle plate 10 is bonded with an adhesive to thepressure chamber plate 20 subjected to etching. When the bonding isconducted, the nozzles 11 are positioned so as to be disposed inrespective spaces of the pressure chambers 21. The pressure chamberplate 20 with the nozzle plate 10 bonded thereto is attached to a case(not shown in the figure) and the ink-jet recording head 1 is obtained.

[0096] (Manufacturing Method of the Second Embodiment)

[0097]FIG. 11 is a cross-sectional schematic view illustrating a methodfor the manufacture of the piezoelectric element and the ink-jetrecording head of the second embodiment. This figure shows the part ofthe process corresponding to FIG. 5 of the first embodiment. In theprocess of the second embodiment, the steps other than the steps S3through S5 of the first embodiment are the same as in the firstembodiment and the explanation thereof is omitted.

[0098] Step of Forming a First Ti Layer (S3)

[0099] After the bottom electrode 33 of Ir and Pt is formed in the samemanner as in S2 of the first embodiment, a step of forming a first Tilayer in which a Ti layer (nucleus) is formed on the bottom electrode 33is immediately implemented. For example, a Ti layer is formed to athickness of no less than 2 nm and no more than 18 nm by a sputteringmethod or the like. The first Ti layer is formed uniformly on the bottomelectrode 33, but it may also have an island-like structure.

[0100] Step of Patterning of the Bottom Electrode (S4)

[0101] Masking is then conducted to a desired shape in order to separatethe bottom electrode 33 and the wiring electrode 33 a, and patterning isperformed by etching on the outside thereof. More specifically, first, aresist material having a uniform thickness is coated on the bottomelectrode by a spinner method, a spray method, or the like (not shown inthe figures). Then a mask is formed according to the shape of thepiezoelectric element and then a resist pattern is formed on the bottomelectrode by exposure and development (not shown in the figures). Thebottom electrode 33 is then etched out by an ion milling or a dryetching method usually used therefor and the ZrO₂ film 32 is exposed.

[0102] Then, cleaning by a reverse sputtering (not shown in the figures)is conducted to remove contaminants or oxidized portions that adhered tothe bottom electrode surface in the patterning step. In the presentembodiment, the first Ti layer is formed on the bottom electrode 33.Therefore, apparently, the bottom electrode 33 is hardly negativelyaffected by the reverse sputtering process.

[0103] A step of forming a second Ti layer in which a Ti layer (nucleus)is further formed on the bottom electrodes 33 and the ZrO₂ film 32 isthen continuously executed by a sputtering method or the like. Thesecond Ti layer formed herein has a thickness of no less than 1 nm andno more than 2 nm. The thickness of the second Ti layer is preferablyless than the thickness of the first Ti layer. In such a case, thereproducibility of 100 plane orientation degree is high. A sum of thethickness of the first and second Ti layers formed in the two steps isno less than 3 nm and no more than 20 nm.

[0104] Step of Forming a Piezoelectric Film (S5)

[0105] A piezoelectric film 43 is then formed on the bottom electrode33. First, a piezoelectric precursor film is formed by a sol-gel method.More specifically, a sol composed by an organic metal alkoxide solutionis coated on the Ti nucleus by a coating method such as a spin coatingmethod. Then, drying is conducted for a prescribed time period at aprescribed temperature to evaporate the solvent. The drying is followedby pyrolyzing for a prescribed time period at a prescribed temperaturein air for thermal decomposition of organic ligands coordinated with themetal and formation of metal oxide. By repeating the coating, drying,and pyrolyzing steps for a required number of times such as two times, atwo-layer piezoelectric precursor film is obtained. As a result ofdrying and pyrolyzing, metal alkoxide and acetic acid salt present inthe solution form a metal/oxygen/metal network via thermal decompositionof ligands.

[0106] The piezoelectric precursor films are then annealed tocrystallize the piezoelectric film. Due to annealing, the piezoelectricprecursor film changes its structure from amorphous to a rhombohedralcrystal structure and changes to a film demonstrating anelectromechanical conversion effect.

[0107] Repeating several times the above-described formation of thepiezoelectric film and annealing thereof makes it possible to obtain thedesired thickness of the piezoelectric film. For example, the thicknessof the precursor film coated in one annealing operation is 200 nm andthe steps are repeated five times.

[0108] In the piezoelectric film 43 thus formed, a portion above thebottom electrode 33 is affected by the bottom electrode and the Tilayers formed in the first and second steps of forming a Ti layer. Thiscauses the portion of the piezoelectric film has a 100 plane orientationdegree of about 80%. Furthermore, a portion formed in the zone fromwhich the bottom electrode 33 was removed by patterning and where theZrO₂ film 32 was exposed is affected by the second Ti layer. This causesthe portion has a large orientation in 100 plane or 111 plane. Since thePZT on the ZrO₂ film 32 is oriented, the crystallinity of the PZT isgood and the crystal grains are fine. Therefore the probability ofcracking is low.

[0109] (Other Modifications)

[0110] The present invention is not limited to the above-describedembodiments and may be modified for various applications. For example,the piezoelectric element manufactured in accordance with the presentinvention can be employed for manufacture not only of theabove-described ink-jet recording head, but also of nonvolatilesemiconductor memory devices, thin-film capacitors, pyroelectricdetectors, sensors, surface elastic wave optical waveguides, opticalmemory devices, spatial light modulators, ferroelectric devices such asfrequency doublers for diode lasers, dielectric devices, pyroelectricdevices, piezoelectric devices, and electrooptical devices.

[0111] In accordance with the present invention, a 100 plane orientationdegree of piezoelectric films can be obtained with good stability andreproducibility. Therefore, a piezoelectric element having stable andexcellent piezoelectric properties at both a high frequency and a lowfrequency, an inkjet recording head and a printer using the same, andmethod for the manufacture of the piezoelectric element can be provided.

What is claimed is:
 1. A method for the manufacture of a piezoelectricelement, comprising: a step of forming a diaphragm on a substrate; astep of forming a bottom electrode on said diaphragm; a step of forminga first piezoelectric layer constituting a part of a piezoelectric filmon said bottom electrode; a step of patterning said first piezoelectriclayer and said bottom electrode to a prescribed shape; a step of forminga second piezoelectric layer constituting another part of thepiezoelectric film on said first piezoelectric layer that was left bysaid patterning and said diaphragm from which said first piezoelectriclayer was removed; and a step of forming a top electrode on saidpiezoelectric film.
 2. The method for the manufacture of a piezoelectricelement according to claim 1, wherein the thickness of said firstpiezoelectric layer is less than the thickness of said secondpiezoelectric layer.
 3. The method for the manufacture of apiezoelectric element according to claim 1, additionally comprising astep of forming a Ti layer after said step of patterning and prior tosaid step of forming a second piezoelectric layer, wherein said Ti layerhas a thickness of no less than 1 nm and no more than 4 nm.
 4. A methodfor the manufacture of a piezoelectric element, comprising: a step offorming a diaphragm on a substrate; a step of forming a bottom electrodeon said diaphragm; a step of forming a first Ti layer on said bottomelectrode; a step of patterning said bottom electrode to the prescribedshape; a step of forming a second Ti layer on the bottom electrode thatwas left by said patterning and said diaphragm from which the bottomelectrode was removed; a step of forming a piezoelectric film on thebottom electrode on which said second Ti layer was formed; and a step offorming a top electrode on said piezoelectric film.
 5. The method forthe manufacture of a piezoelectric element according to claim 4, whereinthe thickness of said first Ti layer formed by said step of forming afirst Ti layer is greater than the thickness of said second Ti layerformed in said step of forming a second Ti layer.
 6. The method for themanufacture of a piezoelectric element according to claim 4, wherein thesum of the thickness of said first and second Ti layers formed in saidsteps of forming Ti layers is no less than 3 nm and no more than 20 nm.7. A method for the manufacture of an ink-jet recording head comprisinga piezoelectric element obtained by a method described in claim 1 or 4,comprising the steps of: etching said substrate and forming pressurechambers; and forming a nozzle plate covering said pressure chambers. 8.A piezoelectric element in which a diaphragm, a bottom electrode, apiezoelectric film, and a top electrode are successively stacked on asubstrate, wherein said bottom electrode is patterned to a prescribedshape, wherein said piezoelectric film is formed on the bottom electrodethat was left by the patterning and the diaphragm from which the bottomelectrode was removed, and wherein a portion of said piezoelectric film,which was formed on the bottom electrode that was left by saidpatterning has a larger number of layers than the portion formed on saiddiaphragm from which the bottom electrode was removed.
 9. Apiezoelectric element in which a diaphragm, a bottom electrode, apiezoelectric film, and a top electrode are successively stacked on asubstrate, wherein said bottom electrode is patterned to a prescribedshape, wherein said piezoelectric film is formed on the bottom electrodethat was left by the patterning and the diaphragm from which the bottomelectrode was removed, and wherein said bottom electrode has a uniformthickness.
 10. The piezoelectric element according to claim 8 or 9,wherein, in the portion of said piezoelectric film that was formed onthe bottom electrode, the layers have a continuous crystal structure.11. A piezoelectric element in which a diaphragm, a bottom electrode, apiezoelectric film, and a top electrode are successively stacked on asubstrate, wherein said bottom electrode is patterned to a prescribedshape, wherein said piezoelectric film is formed on the bottom electrodethat was left by the patterning and the diaphragm from which the bottomelectrode was removed, and wherein a portion of said piezoelectric film,which was formed on said diaphragm, has a prescribed orientation. 12.The piezoelectric element according to claim 11, wherein a portion ofsaid piezoelectric film, which was formed on said diaphragm from whichsaid bottom electrode was removed, has a large orientation in a 100plane or a 111 plane.
 13. The piezoelectric element according to claim8, 9 or 11, wherein a portion of said piezoelectric film, which wasformed on the bottom electrode that was left by said patterning, has a100 plane orientation degree of no less than 70%.
 14. An ink-jetrecording head, comprising: the piezoelectric elements described inclaim 8, 9 or 11; pressure chambers whose internal volume is changed bymechanical displacement of said piezoelectric elements; and ejectionopenings linked to said pressure chambers and ejecting ink droplets. 15.An ink-jet printer comprising the ink-jet recording head described inclaim 14 in a printing mechanism.